In the production of yarn, roving frames are used to transform sliver into roving which is wound on bobbins in roving frames. In a typical construction of such frames, two rows of spindles are provided on a vertically displaceable spindle rail and the spindles can be associated with flyers which receive drafted sliver downstream from a drafting frame and which serve to apply the roving to the bobbins.
The bobbins are wound on bobbin tubes, cores or core sleeves which, for that purpose, must be mounted on the spindle. It is a common practice to suspend the empty core tube from a hanger and to transfer the core tube from that hanger to the spindle, e.g. by a vertical movement of the spindle rail. Similarly, the full bobbin on the spindle may be transferred to a hanger by such a movement of the bobbin rail.
The hangers can be provided with latch or gripper mechanisms which engage in the upper ends of the empty core tubes or the fully-wound core tube, i.e. the core tube carrying the bobbin, and this mechanism may operate with an up and down movement of the core tube relative to the hanger to, for example, engage or latch the core tube in the hanger upon an initial upward movement and downward movement of the core tube and to release the core tube in another axial displacement of the core tube. The process is referred to as a change-over since it allows a core tube carried by a hanger to be seated on a spindle or a core tube carrying a full bobbin to be picked up from a spindle in the roving frame. Of course at a location outside the roving frame or outside the roving winding region, full bobbins are removed from hangers and these hangers may be supplied with empty core tubes.
There are mechanisms for automatically supplying the roving frame with empty core tubes and replacing fully-wound bobbins by such empty core tubes automatically (see DE 36 30 214 C). The core tubes fed to the hangers can be transferred to the spindles by raising the spindle rail and then lowering it. Similarly the full bobbins can be affixed on the hangers by raising the spindle rail, when the spindle carry such full bobbins, and then lowering it.
In the automatic transfer of empty roving core tubes to the bobbin carriers in the spindle rail of a roving frame, the hangers can be switched over by the upward movement of the core tubes.
During this process, the core tubes should have devices for entraining each core tube with the spindle in appropriate engagement. For this purpose, axially-extending teeth in a gear crown can be provided at the bottom of a core tube and can be interdigitated with a plurality of upstanding pins on the bobbin carrier.
The flanks of the pins and the teeth are so beveled that the two can interdigitate easily. In practice, however, this type of registry does not always occur and it is possible for the core sleeve to rest upon the tips of the pins and thus to seat somewhat higher, relative to the spindle, than is desirable during a changeover operation. In this case, with the axial movement of the core tube to release it from the latch of the hanger, the hanger disengages without full seating of the core tube on the spindle and the core tube can fall freely at least to a limited extent. When the fall is greater than the stroke required to latch or release the hanger, the core sleeve may be reengaged by the hanger and then not properly deposited on the spindle. The result is a failure in the changeover process and can lead to problems in machine operation and in the yarn-making process.